News Release Number: STScI-1998-08

Shock Wave Sheds New Light on Fading Supernova

The full news release story:

NASA's Hubble Space Telescope is giving astronomers a ringside seat to a never before seen titanic collision of an onrushing stellar shock wave with an eerie glowing gas ring encircling a nearby stellar explosion, called supernova 1987A.

Though the star's self-destruction was first seen nearly 11 years ago on Feb. 23, 1987, astronomers are just now beginning to witness its tidal wave of energy reaching the "shoreline" of the immense light-year wide ring.

Shocked by the 40-million mile per hour sledgehammer blow, a 100-billion mile diameter knot of gas in a piece of the ring has already begun to "light up", as its temperature surges from a few thousand degrees to a million degrees Fahrenheit.

"We are beginning to see the signature of the collision, the hammer hitting the bell. This event will allow us to validate ideas we have built up over the past ten years of observation," says Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, MA. "By lighting up the ring, the supernova is exposing its own past."

Astronomers predict it's only a matter of years before the complete ring becomes ablaze with light as it absorbs the full force of the crash.

Illuminating the surrounding space like a flashlight in a smoky room, the glowing ring is expected to literally shed a brilliant new light on many unanswered mysteries of the supernova: What was the progenitor star? Was it a single star or binary system? Are a pair of bizarre outer rings attached to an invisible envelope of gas connecting
the entire system?

"We have a unique opportunity to probe structure around the supernova and uncover new clues to the final years of the progenitor star before it exploded," adds Richard McCray of the University of Colorado in Boulder, CO. "The initial supernova flash only lit up a small part of the gas that surrounds the supernova. Most of it is still invisible. But the light from the crash will give us a chance to see this invisible matter for the first time, and then perhaps we can unravel the mystery of the outer rings."

Though scientists will never solve the paradox of what happens when an irresistible force meets an immovable object, the supernova collision is the closest real-world example yet. "This supernova gives us an unprecedented opportunity to directly witness new physics of shock interactions," says McCray. "Though astronomers have measured shock effects from the expanding debris of many supernovae which are
centuries-old, their impact velocities are at least ten times slower than the ones we see today in supernova 1987A."

The ring was formed 20,000 years before the star exploded. One theory is that it resulted from stellar material flung off into space as the progenitor star devoured a stellar companion. The ring's presence was given away when it was heated by the intense burst of light from the 1987 explosion. The ring has been slowly fading ever
since then as the gas cools.

Several years ago radio waves and X-rays were detected as the fastest moving explosion debris slammed into cooler invisible gas inside the ring. In spring of 1997 the newly installed Space Telescope Imaging Spectrograph (STIS) first measured the speed of the supernova debris pushing along the shock wave. "The STIS lets you see the invisible stuff," says George Sonneborn of Goddard Space Flight Center in Greenbelt, MD. "We see the shock happening everywhere around the ring." In July, Hubble Wide Field and Planetary Camera-2 images taken by Robert Kirshner and co-investigators showed that a compact region on the ring lit up like a sparkling diamond set in an engagement ring.

Supernova 1987A is the brightest stellar explosion seen since Johannes Kepler observed a supernova in the year 1604. It is located about 167,000 light-years from Earth in the Large Magellanic Cloud.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.